Tire inner liner and pneumatic tire

ABSTRACT

To provide a tire inner liner formed by using a cylindrical film ( 10 ) including a thermoplastic material and obtained by inflation molding, in which a ratio of breaking strength in a tire width direction ( 14 ) to breaking strength in a tire circumferential direction ( 18 ) of the cylindrical film ( 10 ) is from 1.35 to 1.80. A pneumatic tire ( 1 ) is obtained by extruding and molding the cylindrical film ( 10 ) in which a ratio of breaking strength in an extrusion direction ( 12 ) to breaking strength in a direction perpendicular to the extrusion direction ( 16 ) is from 1.35 to 1.80 by inflation molding using a thermoplastic material, forming a green tire by placing the obtained cylindrical film ( 10 ) on a forming drum so that the extrusion direction ( 12 ) becomes the tire width direction ( 14 ), and vulcanizing and molding the green tire.

TECHNICAL FIELD

The present invention relates to a tire inner liner and a pneumatic tireusing the same.

BACKGROUND ART

An inner liner is provided as an air permeation suppression layer in aninside surface of a pneumatic tire for keeping an air pressure of thetire in a fixed pressure. Such inner liner is generally formed of arubber layer such as a butyl rubber or a halogenated butyl rubber, whichis hardly permeated by a gas. The use of a film made of resin which canbe reduced in thickness is considered for reducing the weight of thetire.

For example, there is disclosed in PTL 1, a pneumatic tire using acylindrical thermoplastic film having no joint fabricated by aninflation molding method as an inner liner. In PTL 2, there aredisclosed that a thermoplastic elastomer film is fabricated by using athermoplastic elastomer composition containing a crosslinked elastomercomponent as a dispersed phase in a continuous phase of a thermoplasticresin by using cylindrical inflation molding, that biaxial stretching isperformed with a blow ratio of 2 or more is performed at the inflationmolding, and that the obtained elastomer film is used for the innerliner of the pneumatic tire. In PTL 3, there are disclosed that a tireinner liner is fabricated by the inflation molding method using athermoplastic elastomer containing a thermoplastic resin and anelastomer component and that a ratio of breaking strength of the innerliner between a tire width direction and a peripheral direction isrespectively from 0.75 to 1.3.

CITATION LIST Patent Literature

-   PTL 1: JP-A-8-258506-   PTL 2: JP-A-2006-315339-   PTL 3: JP-A-2007-030691

SUMMARY OF INVENTION Technical Problem

It has been known that the cylindrical film including the thermoplasticmaterial and obtained by the inflation molding is used as the tire innerliner as described above, in which the inner liner having an orientationratio as the ratio of breaking strength between the tire width directionand the peripheral direction is close to 1 has been used.

However, it has been found that it is difficult to realize both tireformability and tire durability in the inner liner having theorientation ratio close to 1.

In view of the above, an object of the present invention is to provide atire inner liner and a pneumatic tire using the same capable ofrealizing both tire formability and tire durability.

Solution to Problem

According to an embodiment of the present invention, there is provided atire inner liner formed using a cylindrical film that includes athermoplastic material and is obtained by inflation molding, in which aratio of breaking strength in a tire width direction to breakingstrength in a tire circumferential direction of the cylindrical film isfrom 1.35 to 1.80. A pneumatic tire according to an embodiment of thepresent invention includes the tire inner liner.

According to an embodiment of the present invention, there is provided amethod of manufacturing a pneumatic tire including the steps ofextruding and molding a cylindrical film in which a ratio of breakingstrength in an extrusion direction to breaking strength in a directionperpendicular to the extrusion direction is from 1.35 to 1.80 byinflation molding using a thermoplastic material, forming a green tireby placing the obtained cylindrical film on a forming drum so that theextrusion direction becomes a tire width direction, and vulcanizing andmolding the green tire.

Advantageous Effects of Invention

According to the embodiment of the invention, the orientation directionof the cylindrical film obtained by inflation molding is approximatelyparallel to a load direction of the tire, therefore, tire durability isexcellent. Though the cylindrical film is expanded mainly in the tirecircumferential direction at the time of forming the tire, the tirecircumferential direction is a direction perpendicular to theorientation direction of the cylindrical film, and a modulus in adirection perpendicular to the orientation direction is lower than amodulus in a direction parallel to the orientation direction, therefore,the film is easily expanded in the tire circumferential direction andthe tire formability is excellent. Accordingly, both the tireformability and the tire durability can be realized.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a pneumatic tire according to anembodiment.

FIG. 2 is conceptual diagrams showing a relation between a tirecircumferential direction and an orientation direction of a cylindricalfilm according to the embodiment.

FIG. 3 is a conceptual diagram showing a relation between a tire loaddirection and the orientation direction of the cylindrical filmaccording to the embodiment.

FIG. 4 is a conceptual diagram showing a relation between a tire loaddirection and an orientation direction of a film according to acomparative example.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be explained inreference to the drawings.

FIG. 1 is a cross-sectional view of a pneumatic tire 1 according to anembodiment. As shown in the drawing, the pneumatic tire 1 includes aright-and-left pair of bead portions 2, 2 to be rim-assembled, a pair ofsidewall portions 3, 3 extending from the bead portions 2 to the outsideof a tire radial direction, a tread portion 4 provided between the pairof sidewall portions 3, 3 and contacting a road surface, and aright-and-left pair of shoulder portions 5, 5 forming boundary areasbetween the tread portion 4 and the sidewall portions 3, 3 on bothsides.

In the pair of bead portions 2, 2, ring-shaped bead cores 6 arerespectively embedded. A carcass ply 7 using an organic fiber cord islocked with folded around the bead cores 6, 6 and is provided so as tobridge between the right and left bead portions 2, 2 in a toroidalmanner. On an outer peripheral side of the carcass play 7 in the treadportion 4, a belt 8 formed of two pieces of crossing belt plies using arigid tire cord such as a steel cord or aramid fibers is provided.

An inner liner 9 is provided inside the carcass ply 7 over the entireinner surface of the tire. That is, the inner liner 9 is placed so as tocover the entire inner surface of the tire from the tread portion 4toward the bead portions 2, 2 through the shoulder portions 5, 5 and thesidewall portions 3, 3 on the right and left both sides. In theembodiment, an air permeation resistant film formed of a thermoplasticmaterial is used as the inner liner 9. The inner liner 9 is adhered toan inner surface of the carcass ply 7 as shown in an enlarged view inFIG. 1, and more specifically, the inner liner 9 is adhered to an innersurface of a topping rubber layer covering the cord of the carcass ply7.

As a material of the film forming the inner liner 9, various types ofthermoplastic resins and/or thermoplastic elastomers can be used.

As specific examples of thermoplastic resins, polyamide-based resinssuch as nylon 6 and nylon 66, polyester-based resins such aspolybutylene terephthalate (PBT) and polyethylene terephthalate (PET),polynitrile-based resins such as polyacrylonitrile (PAN) andpolymethacrylonitrile, cellulose-based resins such as cellulose acetateand cellulose acetate butyrate, fluorine-based resins such aspolyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), imide-basedresins such as aromatic polyimide (PI), polyvinyl alcohol and so on canbe cited, and above resins can be used independently as well as used bycombining two or more kinds of resins.

As thermoplastic elastomers, block copolymers having hard segmentsforming a thermoplastic frozen phase or crystal phase and soft segmentsindicating rubber elasticity can be used. For example, a polyester-basedelastomer having polyester as a hard segment, a polyamide-basedelastomer having polyamide as a hard segment, a polystyrene-basedelastomer having polystyrene as a hard segment, a polyolefin-basedelastomer having polyethylene or a polypropylene as a hard segment, apolyurethane-based elastomer having a urethane structure as a hardsegment and so on can be cited, and above elastomers can be usedindependently as well as used combining two or more kinds of elastomers.Moreover, materials obtained by blending the block copolymers with arubber component or a resin component can be also used as thermoplasticelastomers. Furthermore, elastomers having a sea-island structureobtained by blending the thermoplastic resins with a rubber componentmay be used as thermoplastic elastomers.

Various types of additives such as fillers and compatibilizers may beblended with the above thermoplastic resins or the thermoplasticelastomers. The same applies to the rubber component included in thethermoplastic elastomer. When these materials are blended, various typesof kneading machines such as a twin-screw extruder, a screw extruder, akneader and a Banbury mixer can be used.

As one embodiment, a film formed of a continuous phase (matrix phase) ofa thermoplastic elastomer (A) and a dispersed phase (domain phase) of arubber (B) is preferably used for the inner liner 9. The material hardlypermeated by air as compared with rubber is selected as thethermoplastic elastomer which forms the continuous phase, therebyimproving the air permeation resistance of the film. As thethermoplastic elastomer is generally softer than the thermoplasticresin, a softer film can be fabricated without substantially increasinga ratio of the rubber forming the dispersed phase. Therefore, both theair permeation resistance and flexibility can be easily realized.

As the thermoplastic elastomer (A) forming the continuous phase, theelastomers enumerated above can be used, and a thermoplasticpolyester-based elastomer (A1) is preferably used from a viewpoint ofheat resistance.

In the thermoplastic polyester-based elastomer (A1), polyester as thehard segment is formed by making a dicarboxylic acid reacting with adiol. As the dicarboxylic acid, an aromatic dicarboxylic acid ispreferably used. As the aromatic dicarboxylic acid, a normal aromaticdicarboxylic acid is widely used. As a principal aromatic dicarboxylicacid, a terephthalic acid or a naphthalene dicarboxylic acid ispreferable, though not particularly limited. As other acid components,aromatic dicarboxylic acids such as an isophthalic acid, a diphenyldicarboxylic acid and a 5-sodium sulfoisophthalic acid, alicyclicdicarboxylic acids such as a cyclohexanedicarboxylic acid and atetrahydrophthalic anhydride, aliphatic dicarboxylic acids such as asuccinic acid, a glutaric acid, an adipic acid, an azelaic acid, asebacic acid, a dodecanedioic acid, a dimer acid and a hydrogenateddimer acid and so on can be cited. These other acid components are usedin a range where a melting point of the polyester-based elastomer is notsignificantly decreased, and a quantity thereof is preferably lower than30 mol %, and more preferably lower than 20 mol % of the entire acidcomponent.

As the diol, an aliphatic or alicyclic diol can be used. As thealiphatic or alicyclic diol, a common aliphatic or alicyclic diol isused, and it is preferable to use alkylene glycols having from 2 to 8carbon atoms principally, though not particularly limited. Specifically,an ethylene glycol, a 1,3-propylene glycol, a 1,4-butanediol, a1,6-hexanediol, a 1,4-cyclohexanedimethanol and so on can be cited.Among them, the 1,4-butanediol and/or the 1,4-cyclohexanedimethanol aremost preferable.

As components forming the polyester as the hard segment, componentshaving a butylene terephthalate unit, a butylene isophthalate unitand/or a butylene naphthalate unit are preferable from viewpoints ofphysicality, formability and cost performance. In the case of thenaphthalate unit, a 2,6-form is preferable.

In the thermoplastic polyester-based elastomer (A1), examples of theconstituent component of soft segment include a polyester, a polyether,a polycarbonate and so on. Among them, a polyester-based elastomerhaving polycarbonate as the soft segment is preferably used as both airpermeation resistance and flexibility are well balanced. As apolycarbonate, an aliphatic polycarbonate diol produced from a carbonicester such as a dimethyl carbonate or a diethyl carbonate and aaliphatic glycol having from 2 to 12 carbon atoms and so on can becited.

As the thermoplastic polyester-based elastomer (A1), it is particularlypreferable to use the elastomer having a hard segment principallycomprising polybutylene terephthalate and a soft segment comprisingaliphatic polycarbonate. A ratio between the hard segment and the softsegment is not particularly limited in the thermoplastic polyester-basedelastomer (A1), however, a mass ratio is preferably hard segment:softsegment=30:70 to 95:5, and more preferably, in a range of 40:60 to90:10.

The thermoplastic polyester-based elastomer (A1) may be a blockcopolymer having the hard segment and the soft segment, and may be anelastomer obtained by blending a resin forming an additional hardsegment such as polybutylene terephthalate with the block copolymer, aswell as an elastomer obtained by further copolymerizing the resin withthe block copolymer. In this case, it is also possible to generate acopolymer by melting and kneading the block copolymer and the resin suchas polybutylene terephthalate. Accordingly, the copolymer obtained bymelting and kneading as well as the copolymer obtained only by blendingmay be adopted.

As the rubber (B) forming the dispersed phase, various types of rubberscommonly used by being crosslinked (vulcanized) are adopted. Forexample, diene-based rubbers and hydrogenated rubbers thereof such as anatural rubber (NR), an epoxidized natural rubber (ENR), an isoprenerubber (IR), a styrene-butadiene rubber (SBR), a butadiene rubber (BR),a nitrile rubber (NBR), a hydrogenated nitrile rubber (H-NBR) and ahydrogenated styrene-butadiene rubber; olefin-based rubbers such as anethylene-propylene rubber (EPDM), a maleic acid-modifiedethylene-propylene rubber, a maleic acid-modified ethylene-butylenerubber, a butyl rubber (IIR) and an acrylic rubber (ACM);halogen-containing rubbers such as a halogenated butyl rubber (forexample, a brominated butyl rubber (Br-IIR), a chlorinated butyl rubber(Cl-IIR)), a chloroprene rubber (CR) and a chlorosulfonatedpolyethylene; and a silicon rubber, a fluororubber, a polysulfide rubberand so on can be cited. Any one of these kinds of rubbers may be usedindependently as well as used by combining two or more kinds of rubbers.In the above rubbers, it is preferable to use at least one kind selectedfrom the butyl rubber (IIR), the halogenated butyl rubber such as thebrominated butyl rubber (Br-IIR), the nitrile rubber (NBR) and thehydrogenated nitrile rubber (H-NBR) from a viewpoint of the airpermeation resistance.

The rubber (B) forming the dispersed phase may be any one kind of or ablend of two kinds or more of the above-described rubber polymers.Various kinds of compounding agents commonly compounded to a rubbercomposition such as a filler, a softener, an antioxidant, a processingaid and a crosslinking agent may be added to those rubbers. That is, therubber (B) to be the dispersed phase may be a rubber formed of a rubbercomposition obtained by adding various compounding agents to the rubber.

A compounding ratio (a ratio as polymer components except compoundingagents such as the filler) between the thermoplastic elastomer (A) andthe rubber (B) is not particularly limited, and for example, from 90/10to 30/70 in mass ratio (A)/(B), and more preferably, from 70/30 to40/60.

The thermoplastic material forming the film according to the embodimentmay contain a compatibilizer in addition to the thermoplastic elastomer(A) and the rubber (B). The compatibilizer reduces an interfacialtension between the thermoplastic elastomer (A) and the rubber (B) tocompatibilize the both, which can reduce the particle size of thedispersed phase and improve the film formability. As compatibilizers, agraft copolymer with a polycarbonate resin as a main chain and with amodified acrylonitrile-styrene copolymer resin as a side chain,copolymers having an ethylene main chain backbone and a side chaincontaining an epoxy group (for example, ethylene copolymers containingthe epoxy group such as an ethylene-glycidyl (meth)acrylate copolymer(namely, an ethylene-glycidyl methacrylate copolymer and/or anethylene-glycidyl acrylate copolymer)), a graft copolymer with theethylene-glycidyl (meth)acrylate as a main chain and with a polystyreneresin as a side chain and so on can be cited. A compounding amount ofthe compatibilizer is not particularly limited, and can be from 0.5 to10 parts by mass, per 100 parts by mass of the total amount of thethermoplastic elastomer (A) and the rubber (B).

As a more preferred embodiment, a film obtained by melting and kneadingthe thermoplastic elastomer (A) and the rubber (B) with a crosslinkingagent so that the rubber is dynamically crosslinked by the crosslinkingagent is used as the inner liner 9. The rubber (B) is dynamicallycrosslinked (TPV), thereby reducing the particle size of the dispersedphase and improving flexibility.

As crosslinking agents for dynamically crosslinking the rubber,vulcanizing agents such as sulfur and sulfur-containing compounds,vulcanization accelerators, phenolic resins and so on can be cited. Thephenolic resins are preferably used from a viewpoint of heat resistance.As phenolic resins, resins obtained by condensation reaction of phenolsand formaldehyde can be cited, and more preferably, an alkylphenol-formaldehyde resin is used. A compounding amount of thecrosslinking agent is not particularly limited as long as they cancrosslink the rubber (B) properly, but the amount is preferably from 0.1to 10 parts by mass, per 100 parts by mass of the rubber (B) (the amountof the polymer except the compounding agents such as the filler).

The film formed of the continuous phase of the thermoplastic elastomer(A) and the dispersed phase of the rubber (B) is preferably an airpermeation coefficient of 5×10¹³ fm²/Pa·s or less for enhancing theweight reducing effect of the tire. More preferably, the air permeationcoefficient is 4×10¹³ fm²/Pa·s or less. The lower limit is notparticularly limited, however, 0.5×10¹³ fm²/Pa·s or more is practicallypreferable. Here, the air permeation coefficient is a value measuredunder conditions of a test gas:air and a test temperature: 80° C. basedon JIS K7126-1 “Plastics-Film and sheeting-Determination of gastransmission rate-Part 1: Differential-pressure method”.

It is also preferable that the film has 10 MPa or less in 10% modulusfor enhancing follow-up ability to improve workability at the time oftire forming and enhancing tire durability. More preferably, the 10%modulus is 8 MPa or less, and further preferably 6 MPa or less. Thelower limit is not particularly limited, however, 3 MPa or more ispreferable. Here, the 10% modulus is a tensile stress measured based ona tensile test of JIS K6251 in 23° C. at the time of 10% stretch(punched by No. 3 dumbbell), which is a tensile stress measured in adirection perpendicular to an extrusion direction of the film (tirecircumferential direction).

In the embodiment, the cylindrical film obtained by the inflationmolding is used as the film forming the inner liner 9. That is, thecylindrical film for the inner liner is obtained by melding and kneadingthe thermoplastic materials and by extrusion-molding the obtained moltenmaterial into the cylindrical shape by using an extruder provided withan inflation die such as a ring die. At that time, the inflation moldingis performed so that the cylindrical film has a given orientation bysetting an extrusion direction to an orientation direction, that is, thefilm has the orientation in which breaking strength becomes the maximumin the extrusion direction and becomes the minimum in a directionperpendicular to the extrusion direction in the embodiment.

In the cylindrical film according to the embodiment, a ratio of abreaking strength in the extrusion direction to a breaking strength inthe direction perpendicular to the extrusion direction, that is, a ratio(orientation ratio) of the breaking strength, “extrusiondirection”/“direction perpendicular to the extrusion direction” is from1.35 to 1.80. The cylindrical film is set so that the extrusiondirection becomes a tire width direction in the embodiment. Therefore, aratio of the breaking strength in the tire width direction to thebreaking strength in the tire circumferential direction, that is, aratio of the breaking strength, “tire width direction”/“tirecircumferential direction” is from 1.35 to 1.80 in the tire inner liner.As the orientation ratio of the breaking strength is 1.35 or more, boththe tire formability and the tire durability can be realized. When theorientation ratio of the breaking strength exceeds 1.80, a crackextending in the tire width direction easily occurs while the tire isrunning. The orientation ratio of the breaking strength is preferablyfrom 1.35 to 1.50.

The breaking strength of the cylindrical film in the extrusion direction(tire width direction) is preferably 15 MPa or more, and more preferably18 MPa or more. The upper limit of the breaking strength in theextrusion direction is not particularly limited, but the breakingstrength is preferably 25 MPa or less, and more preferably 22 MPa orless.

Here, the breaking strength of the film is a tensile strength measuredbased on the tensile test of JIS K6251 in 23° C. (punched by No. 3dumbbell), which is measured in the extrusion direction of the film(tire width direction) and the direction perpendicular to the extrusiondirection (tire circumferential direction).

In the cylindrical film according to the embodiment, a ratio of the 10%modulus in the extrusion direction to the 10% modulus in the directionperpendicular to the extrusion direction, that is, a ratio (orientationratio) of the 10% modulus, “extrusion direction”/“directionperpendicular to the extrusion direction” is preferably from 1.1 to 1.5.The cylindrical film is set so that the extrusion direction becomes thetire width direction in the embodiment. Therefore, a ratio of 10%modulus in the tire width direction to 10% modulus in the tirecircumferential direction, namely, a ratio of the 10% modulus, “tirewidth direction”/“tire circumferential direction” is preferably from 1.1to 1.5. The film is expanded mainly in the tire circumferentialdirection at the time of tire forming. The 10% modulus in the tirecircumferential direction is lower when the orientation ratio of the 10%modulus is higher, therefore, the tire forming is easier. It ispreferable that the orientation ratio of the 10% modulus is from 1.1 to1.3.

As a condition of the inflation molding, a blow ratio is preferably from1.2 to 1.8 for obtaining the above orientation ratio. Here, the blowratio is a ratio between a diameter of a ring die and a diameter of theexpanded cylindrical film in the inflation method, which is referred toalso as blowup rate. The formability in the inflation molding can beimproved by setting the blow ratio to 1.2 or more. When the blow ratiois 1.8 or less, the orientation ratios in the breaking strength and the10% modulus can be increased. More preferably, the blow ratio is from1.2 to 1.6.

Also as a condition of the inflation molding, a taking-up speed of thecylindrical film extruded from the extruder is preferably from 1 to 10m/minute, and more preferably 2 to 8 m/minute. A temperature in themolding may be a temperature in which the thermoplastic material ismelted or more.

As a preferred embodiment, when a dynamically crosslinked material ofthe thermoplastic elastomer (A) and the rubber (B) is used as thethermoplastic material, the cylindrical film is fabricated in thefollowing manner. That is, the thermoplastic elastomer (A) and therubber (B) are melted and kneaded with a crosslinking agent, and therubber (B) is dynamically crosslinked by the crosslinking agent toobtain the thermoplastic material including the rubber (B) as thedispersed phase in the continuous phase of the thermoplastic elastomer(A). After that, the film is formed by the inflation molding whilemelting the obtained thermoplastic material.

A thickness of the cylindrical film obtained by the inflation molding isnot particularly limited, and may be set to, for example, from 0.02 to2.0 mm, and more preferably set to from 0.05 to 1.0 mm.

An obtained cylindrical film 10 is set in the tire 1 so that the widthdirection thereof (namely, an extrusion direction 12) corresponds to atire width direction 14 and a circumferential direction (namely, adirection 16 perpendicular to the extrusion direction) corresponds to atire circumferential direction 18 as shown in FIG. 2. In more detail,the cylindrical film 10 is attached to an outer periphery of a formingdrum as a member forming the inner liner 9 so that the extrusiondirection 12 corresponds to the tire width direction 14 at the time offorming a green tire. The carcass ply 7 is adhered thereto, and further,the belt 8 and respective tire members such as a tread rubber and asidewall rubber are adhered so as to be overlapped, and these membersare inflated to fabricate a green tire (unvulcanized tire), and thepneumatic tire 1 is obtained by vulcanizing and molding the green tirein a mold.

In the obtained pneumatic tire 1, the inner liner 9 is set so that theextrusion direction (namely, the orientation direction) 12 of thecylindrical film 10 corresponds to the tire width direction 14.Accordingly, the orientation direction 12 of the cylindrical film 10 isparallel to a tire meridian direction, specifically, the orientationdirection 12 is arranged so as to be approximately parallel to the tirewidth direction in the tread portion 4, and the orientation direction 12is arranged so as to be approximately parallel to the tire radialdirection in the shoulder portion 5, the sidewall portion 3 and the beadportion 2.

[Operations and Effects]

Next, operations and effects of the above embodiment will be explained.

In the pneumatic tire 1 according to the embodiment, the inner liner 9is arranged so that the orientation direction 12 of the cylindrical film10 corresponds to the tire width direction 14 and the orientationdirection 12 is approximately parallel to the tire radial direction inthe area from the shoulder portion 5 to the sidewall portion 3. The tirerepeats a deformation in which the area from the shoulder portion 5 tothe sidewall portion 3 is bent by a load and returns to the originalshape at the time of rolling. That is, bending deformation of the tireoccurs in the area from the shoulder portion 5 to the sidewall portion 3in the load direction. In the embodiment, in the area where such bendingdeformation is performed, a load direction 20 and the orientationdirection 12 of the cylindrical film 10 are approximately parallel asshown in FIG. 3. Accordingly, a fracture due to bending deformation atthe time of rolling the tire hardly occurs in the inner liner 9 and thedurability is improved.

On the other hand, a pneumatic tire according to a comparative exampleis considered, in which a cylindrical film is fabricated using the filmhaving the orientation in the extruding direction formed by a T-dieextrusion method so that the extrusion direction becomes a tirecircumferential direction and is used as the inner liner. In the tireaccording to the comparative example, an orientation direction(extrusion direction) 24 of the film is perpendicular to a tire loaddirection 22 as shown in FIG. 4. Accordingly, when the area from theshoulder portion to the sidewall portion is bent and deformed in theload direction at the time of rolling the tire, a fracture extending inthe tire circumferential direction easily occurs in the film of theinner liner in the vicinity of the shoulder portion, which impairs thedurability.

According to the embodiment, the fracture due to the bending deformationat the time of rolling the tire hardly occurs. When the film formed bythe T-die extrusion method is used, a process of bonding end portions ofthe film to make the cylindrical shape is necessary after the extrusionmolding. However, the film is extruded in the cylindrical shape in theinflation molding used in the embodiment, therefore, such bondingprocess is not necessary. In the case of the T-die extrusion method, forexample, when the end portions are bonded by using heat sealing, thethickness of film approximately doubles at a joint, the probability thatthe joint is damaged in a tire durability test increases and thedurability is damaged. On the other hand, the cylindrical film having nojoint can be obtained by the inflation molding according to theembodiment, which improves the durability also from this point of view.

Also according to the embodiment, the tire formability is also excellentas the cylindrical film having the given orientation is used as theinner liner. Specifically, the cylindrical film used as the inner linerat the time of forming the green tire is expanded mainly in the tirecircumferential direction. At this time, the tire circumferentialdirection is the direction perpendicular to the orientation direction ofthe cylindrical film in the embodiment, the cylindrical film is easilyexpanded in the tire circumferential direction and the green tire iseasily formed.

The pneumatic tire according to the embodiment is not limited to thepneumatic tire for a passenger car but also can be applied to varioustypes of tires for automobiles including tires of trucks or buses, whichare for heavy loads, and can be applied to various types of tires suchas tires for two-wheeled vehicles including bicycles.

EXAMPLES

Hereinafter, the present invention will be specifically explained basedon examples, and the present invention is not limited by these examples.

Examples 1 to 3, Comparative Examples 1, 2

50 parts by mass of a thermoplastic polyester-based elastomer B, 50parts by mass of a butyl rubber (“IIR268” manufactured by Exxon MobilChemical Company), 5 parts by mass of a compatibilizer (“BONDFAST E”manufactured by SUMITOMO CHEMICAL Co., Ltd.), 2.5 parts by mass of aphenol-based resin (alkyl phenol/formaldehyde condensation product“TACKIROL 201” manufactured by Taoka Chemical Co., Ltd) as acrosslinking agent were prepared, which were dynamically crosslinked bybeing melted and kneaded by a twin-screw kneading machine (manufacturedby Research Laboratory of Plastic Technology Co., Ltd.) so as to bepelletized. 2.5 parts by mass of a resorcin-formaldehyde condensationproduct (modified resorcin-formaldehyde condensation product “SUMIKANOL620” manufactured by Taoka Chemical Co., Ltd) as an adhesive was addedto 107.5 parts by mass of the obtained dynamically crosslinked materialby using the twin-screw kneading machine, and these materials weremelted and kneaded to obtain pellets.

The obtained pellets were extruded into a cylindrical film having athickness of 0.2 mm and a diameter of 360 mm by inflation molding usinga single screw extruder to which a ring die for inflation was attached.In the extrusion molding, the size of the ring die was changed withrespect to respective blow ratios so as to form the cylindrical filmhaving the above size. The molding temperature at the time of inflationmolding was 240° C., and the blow ratios and the taking-up speeds wereas shown in Table 1. All the obtained cylindrical films had thethermoplastic polyester-based elastomer as the continuous phase and thedynamically crosslinked material of butyl rubber as the dispersed phase.Note that the cylindrical film was not able to be obtained by inflationmolding in Comparative Example 1 as the blow ratio was too low.

Example 4

The pellets were obtained by the same method as the embodiments 1 to 3described above except that the thermoplastic polyester-based elastomerA was used instead of using the thermoplastic polyester-based elastomerB. Extrusion molding was performed by using the obtained pellets by theinflation molding (the blow ratio and the taking-up speed were as shownin Table 1). The obtained cylindrical film had the thermoplasticpolyester-based elastomer as the continuous phase and the dynamicallycrosslinked material of butyl rubber as the dispersed phase.

The thermoplastic polyester-based elastomers A and B were synthesized bythe following method.

Thermoplastic polyester elastomer A

(1) Preparation of Polybutylene Terephthalate Copolymer

100 parts by mass of a terephthalic acid, 18.5 parts by mass of anisophthalic acid, 110 parts by mass of a 1,4-butanediol were put into astainless autoclave provided with a stirrer, 56.5 mL of an n-butanolsolution of Tetra-n-butyl Titanate monomer (68 g/L) was added, and thesewere stirred for 2.5 hours at normal pressure and at 180 to 220° C. toperform transesterification. After that, the pressure was reduced fromthe normal pressure to 130 Pa for 20 minutes at 220° C. to distill anexcessive diol component, and polymerization was performed. After 1.5hours passed, the contents were cooled and taken out to obtain anisophthalic acid copolymerized polybutylene terephthalate (polymer “a”).The number average molecular weight of the obtained polymer “a” was38000.

(2) Preparation of Aliphatic Polycarbonatediol

100 parts by mass of an aliphatic polycarbonatediol (“CarbonatediolT6002”, molecular weight 2150, 1,6-hexanediol type manufactured by AsahiKasei Chemicals Corporation) and 7.0 parts by mass of a diphenylcarbonate were respectively prepared, which were reacted at atemperature of 205° C. and 130 Pa. After two hours, the contents werecooled and taken out to obtain aliphatic polycarbonatediol (polymer“b”). The number average molecular weight of the obtained polymer “b”was 7500.

(3) Preparation of Thermoplastic Polyester Elastomer

100 parts by mass of the polymer “a” and 33 parts by mass of the polymer“b” prepared in the above method were stirred at 220 to 245° C., under130 Pa, for 1.5 hours to perform transesterification reaction. Afterconfirming that the resin became transparent, the contents were cooledand taken out. The amount of the hard segment contained in the obtainedthermoplastic polyester elastomer was 75 mass %, and the amount of theisophthalic acid forming the hard segment was 15 mol %. A melting pointwas 187° C. and a Young's modulus was 180 MPa.

Thermoplastic Polyester Elastomer B

A thermoplastic polyester elastomer B′ in which the hard segmentincludes a butylene terephthalate unit and the soft segment includesaliphatic polycarbonatediol (1,6-hexandiol type) was obtained based onthe method described in Example 1 of Japanese Patent No. 4244067.Separately, an isophthalic acid copolymerized polybutylene terephthalate(polymer “c”: the number average molecular weight was 22000) formed ofterephthalic acid/isophthalic acid/1,4-butanediol (molar ratio35/65/100) was obtained in the usual manner. After 25 parts by mass ofthe polymer “c” was added to 100 parts by mass of the thermoplasticpolyester elastomer B′ and these materials were dry blended, the mixturewas melted and kneaded by a TEM-26SS twin-screw extruder (manufacturedby TOSHIBA MACHINE Co., Ltd) under conditions of a temperature 180 to230° C. and a screw speed of 100 rpm to allow the transesterificationreaction to proceed. The amount of the hard segment contained in theobtained thermoplastic polyester elastomer B was 75 mass %, the amountof the isophthalic acid forming the hard segment was 15 mol %. A meltingpoint was 203° C. and a Young's modulus was 235 MPa.

Here, the number average molecular weight of the polymers “a”, “c”(polyester) and the polymer “b” (aliphatic polycarbonatediol) andmelting points of the thermoplastic polyester elastomers A, B weremeasured by the following methods.

The number average molecular weight of Polyester (Mn):

0.05 g of polyester was dissolved in 25 ml of a mixed solvent(phenol/tetrachloroethane=6/4 (mass ratio)), and a reduced viscosityη_(sp)/c at 30° C. was measured by using an Ostwald viscometer. Mn wascalculated in accordance with the following formula by using the valueof the measured reduced viscosity η_(sp)/c.

η_(sp) /c=1.019×10⁻⁴×Mn^(0.8928)−0.0167

The Number Average Molecular Weight of Aliphatic Polycarbonatediol (Mn):

An aliphatic polycarbonatediol sample was dissolved in Deuteratedchloroform (CDCl₃) and ¹H-NMR was measured to calculate an end group,then, Mn was calculated by the following formula.

Mn=1000000/((end group amount(equivalent/ton))/2)

Melting Point (Tm) of Thermoplastic Polyester Elastomer

By using a differential scanning calorimeter DSC220C (2920 manufacturedby TA Instruments Inc.), the thermoplastic polyester elastomerdepressurized and dried at 50° C. for 15 hours was increased intemperature to 250° C. once and melted, then, cooled to 50° C., andincreased in temperature to 20° C./minute again and measured todetermine a peak temperature of an endothermic change by the melting asa melting point. As a measurement sample, 10 mg of the sample wasmeasured in an aluminum pan (2920 manufactured by TA Instruments Inc.)to be in a sealed state by an aluminum lid (2920 manufactured by TAInstruments Inc.) and measured under a nitrogen atmosphere.

Using the obtained cylindrical film, the air permeation coefficient wasmeasured, then, the breaking strength, a breaking elongation and the 10%modulus in the extrusion direction (tire width direction) and thedirection perpendicular to the extrusion direction (tire circumferentialdirection) were measured by performing the tensile test. The results areshown in Table 1. The breaking elongation is a value measured based onthe tensile test of JIS K6251 in the same manner as the breakingstrength and the 10% modulus as described above, which is an elongationat the time of cutting at 23° C. (punched by No. 3 dumbbell). In Table1, the orientation ratio in 10% modulus (M10) is represented by “M10 inthe tire width direction”/“Ml 0 in the tire circumferential direction”,the orientation ratio in the breaking elongation (EB) is represented by“EB in the tire width direction”/“EB in the tire circumferentialdirection”, and the orientation ratio in the breaking strength (TB) isrepresented by “TB in the tire width direction”/“TB in the tirecircumferential direction”.

Using the obtained cylindrical film, the tire formability and the tiredurability were evaluated. An evaluation method is as follows.

Tire formability: the inflation experiment to a shape of the green tirewas performed by winding the film around a tire forming drum. Theexperiment was performed 5 times. When at least one defective formingsuch as peeling occurred, evaluation was made as “X”, and when nodefective forming occurred, evaluation was made as “◯”.

Tire durability: A steel radial tire 195/65R15 was fabricated by usingthe film as the inner liner, and a durability test was performed by adrum-type testing machine by using the obtained tire in conformity withconditions determined in Federal Motor Vehicle Safety Standards FMVSS139, the inner liner film on the inner surface of the tire was visuallychecked after the running test, then, a travelling distance until anydefect such as a fracture, a crack or peeling was recognized wasmeasured. The results are shown by index numbers in which the travellingdistance measured when a normal rubber inner liner (thickness=0.6 mm) isused is set to 100. The larger the numeric value is, the longer thetravelling distance to the defect detection is, which indicates that thedurability is excellent.

Comparative Examples 3, 4

A film having a thickness of 0.2 mm was extruded by a single-screwextruder to which a T-die was attached instead of performing theinflation molding. The used thermoplastic materials were the same as theabove examples. Using the obtained film, the air permeation coefficientwas measured and the tensile test was performed to measure the breakingstrength, the breaking elongation and the 10% modulus in the extrusiondirection and the direction perpendicular to the extrusion direction.Using the obtained film, the tire formability and the tire durabilitywere evaluated. In Comparative Example 3, a cylindrical film wasfabricate by bonding end portions by using heat sealing so that theextrusion direction (orientation direction) of the film becomes the tirewidth direction to be examined in the tests of tire formability test andtire durability. In Comparative Example 4, a cylindrical film wasfabricated by bonding end portions by using heat sealing so that theextrusion direction (orientation direction) of the film becomes the tirecircumferential direction to be examined in the tests of tireformability test and tire durability.

TABLE 1 Comparative Comparative Comparative Comparative Example 1Example 2 Example 3 Example 1 Example 2 Example 4 Example 3 Example 4Film forming method Inflation molding T-die molding Blow ratio 1.2 1.51.8 1.0 3.0 1.5 — — Taking-up speed (m/minute) 6 6 6 6 6 6 1 1 Filmphysical Properties Air permeation coefficient (80° C.) × 3.96 3.96 3.99Inflation 3.98 3.85 3.95 3.92 10¹³(fm²/Pa · s) molding is not Tire widthdirection available 10% modulus (MPa) 5.4 5.3 5.2 5.0 5.8 5.5 4.8Breaking strength (MPa) 19.9 19.5 19.5 19.2 20.6 20.0 14.9 Breakingelongation (%) 470 460 460 430 420 460 450 Tire circumferentialdirection 10% modulus (MPa) 4.5 4.7 4.7 4.8 4.9 4.7 5.5 Breakingstrength (MPa) 14.0 14.3 14.4 16.7 15.0 14.5 20.5 Breaking elongation(%) 460 460 450 440 410 450 460 Orientation ratio of 10% modulus 1.21.13 1.11 1.04 1.18 1.17 0.87 Orientation ratio of breaking elongation1.02 1.0 1.02 0.98 1.05 1.02 0.98 Orientation ratio of breaking strength1.42 1.36 1.35 1.15 1.37 1.38 0.73 Evaluation Tire formability ◯ ◯ ◯ — X◯ ◯ X Tire durability 100 100 100 — 100 100 75 30

The results are as shown in Table 1. In Comparative Example 4, the filmobtained by the T-die extrusion method was used. As the film was set sothat the orientation direction of the film became the tirecircumferential direction, the film was not easily expanded in the tirecircumferential direction and the film was peeled off easily after thefilm expansion, therefore, the tire formability was inferior. In thetire durability test, a fracture extending in the tire circumferentialdirection occurred in the film of the inner liner in the vicinity of theshoulder portion, which reduced the durability. In Comparative Example3, the film obtained by the T-die extrusion method was arranged so thatthe orientation direction became the tire width direction and therigidity in the tire circumferential direction is low, therefore, thetire formability was good. As the orientation direction was the tirewidth direction, the generation of a fracture in the vicinity of theshoulder portion in the tire durability test did not occur. However, thecylindrical film has the joint, film peeling occurred at the joint inthe tire durability test, therefore, the durability was inferior.

In Comparative Example 2, a cylindrical film having an orientation ratioof approximately “1” and obtained by inflation molding was used. As thefilm had no joint, the problem of durability due to the film peeling inthe joint did not occur. However, as the rigidity of the tirecircumferential direction was high, the film was not easily expanded inthe tire circumferential direction and is easily peeled off after thefilm expansion, therefore, the tire formability was inferior.

On the other hand, the cylindrical film having the orientation ratio offrom 1.35 to 1.80 obtained by the inflation molding was used in Examples1 to 4, therefore, both the tire formability and the tire durability canbe realized.

Some embodiments of the present invention have been explained as theabove, and these embodiments were cited as examples, which do not intendto limit the scope of the invention. These novel embodiments can beachieved in other various forms and various omissions, replacements andalterations may occur within a scope not departed from the gist of theinvention. These embodiments and modifications thereof are included inthe scope and the gist of the invention as well as included in theinventions described in claims and a scope equivalent thereto.

REFERENCE SIGNS LIST

-   1 . . . pneumatic tire, 3 . . . sidewall portion, 5 . . . shoulder    portion, 9 . . . inner liner, 10 . . . cylindrical film, 12 . . .    extrusion direction (orientation direction), 14 . . . tire width    direction, 16 . . . direction perpendicular to extrusion direction,    18 . . . tire circumferential direction

1. A tire inner liner formed using a cylindrical film that comprises athermoplastic material and is obtained by inflation molding, wherein aratio of breaking strength in a tire width direction to breakingstrength in a tire circumferential direction of the cylindrical film isfrom 1.35 to 1.80.
 2. The tire inner liner according to claim 1, whereinthe tire inner liner is obtained by the inflation molding with a blowratio of from 1.2 to 1.8.
 3. The tire inner liner according to claim 1,wherein the cylindrical film is formed of a continuous phase of athermoplastic elastomer and a dispersed phase of a rubber.
 4. The tireinner liner according to claim 3, wherein the thermoplastic elastomercomprises a hard segment comprising polybutylene terephthalate and asoft segment comprising aliphatic polycarbonate.
 5. The tire inner lineraccording to claim 4, wherein the hard segment comprises an isophthalicacid copolymerized polybutylene terephthalate.
 6. The tire inner lineraccording to claim 3, wherein the cylindrical film is formed by meltingand kneading the thermoplastic elastomer and the rubber with acrosslinking agent so that the rubber is dynamically crosslinked by thecrosslinking agent.
 7. A pneumatic tire comprising: the tire inner lineraccording to claim
 1. 8. The pneumatic tire according to claim 7,wherein the tire inner liner is arranged so that an orientationdirection as an extrusion direction of the cylindrical film is parallelto the tire width direction in a tread portion and is parallel to a tireradial direction in a sidewall portion.
 9. A method of manufacturing apneumatic tire, comprising: extruding and molding a cylindrical film inwhich a ratio of breaking strength in an extrusion direction to breakingstrength in a direction perpendicular to the extrusion direction is from1.35 to 1.80 by inflation molding using a thermoplastic material;forming a green tire by placing the obtained cylindrical film on aforming drum so that the extrusion direction becomes a tire widthdirection; and vulcanizing and molding the green tire.
 10. The method ofmanufacturing the pneumatic tire according to claim 9, wherein a blowratio is set to from 1.2 to 1.8 when the cylindrical film is formed bythe inflation molding.
 11. The method of manufacturing the pneumatictire according to claim 9, wherein a taking-up speed of the cylindricalfilm extruded from an extruder at the time of the inflation molding isset to from 1 to 10 m/minute.
 12. The method of manufacturing thepneumatic tire according to claim 9, wherein a thermoplastic elastomerand a rubber are melted and kneaded with a crosslinking agent, and therubber is dynamically crosslinked by the crosslinking agent to obtainthe thermoplastic material including the thermoplastic elastomer as acontinuous phase and the rubber as a dispersed phase.